1. Field of the Invention
The present invention relates to a thread-tensioning device on a warp creel, especially for warping and beam warping machines, in which the thread unwound from a bobbin is guided through in a straight line between the discs of a disc brake, the lower disc of which is driven by a drive shaft running outside the disc periphery and the upper disc of which is pressable resiliently against the lower disc, and in which the thread is deflectable, as it leaves the creel, by a deflecting device towards the lapping machine.
2. Description of the Prior Art
A thread-tensioning device of this type is known, for example, from Swiss Patent Specification 452,452. In the case of this known thread-tensioning device, the lower disc of a disc pair rests via a damping disc on a bevel wheel carrying a gearwheel rim which meshes with a pinion on a drive shaft. The disc pair and drive shaft are accommodated completely in an upright creel profile part, U-shaped in cross-section, which supports further disc pairs in the same way. Thread-guide eyelets are provided in the legs of the profile part to guide the thread in a straight line between the discs of each disc pair. After the thread has passed through the second thread-guide eyelet, viewed in the direction of the thread run, it is deflected through about 90.degree. round the margin of the eyelet. Other thread-tensioning devices known, for example, from French Patent Specification No. 2,271,161, use deflecting bars instead of sleeves or eyelets as the deflecting device.
As is known, any deflection of a thread in the warping or beam warping process presents problems, for various reasons. On the one hand, with each deflection, the thread experiences, between its feed and delivery, an increase in tension due to friction at the deflecting device. This increase in tension depends on the design of the deflecting device, on the material used therefor and, of course, also on the thread quality. In addition, a further factor substantially influencing the friction and consequently the thread tension is the increasing soiling of the deflecting device which occurs during operation or even, where the threads always slide at the same point, as is the case, as a rule, with deflecting devices in the form of deflecting bars or thread-guide eyelets, possible wearing of these points. Precisely these last-mentioned factors, which influence the frictional conditions at the deflecting points, are naturally different for each deflecting point, as a result of which, for the threads of a creel which are combined, for example, into a warp section, different tension conditions arise within the warp section and these adversely influence the quality of the warped and where relevant also beam-warped warp.
In addition, when eyelets or deflecting bars are used to deflect the threads, in the case of certain thread qualities, very particularly, for example, in the case of glass threads, fibrils are buckled up during deflection and the threads are damaged by this phenomenon known as "fibril separation".
However, when using thread-tensioning devices of the above-mentioned type, difficulties often arise even with the disc pairs at the warping and beam-warping speeds conventional today and, in the currently likewise conventional universal application of the same thread-tensioning devices, both for natural staple fibers and for textured polyamides and polyesters, glass fibers, etc.
Owing to a frequently insufficient take-up of the upper disc by the running thread, the latter is subjected to a large local wear. At the same time, however, there occur here also, as at the deflecting points, dirt deposits which change the frictional conditions and thereby adversely affect the desired uniformity of the thread tension for all threads processed simultaneously.